Lecture on Cardiac Conduction System and EKG Interpretation

Overview

• The lecture covers the cardiac conduction system and basics of EKG interpretation.
• Essential before learning about dysrhythmias (Chapter 34).
• Reviewed knowledge from anatomy and physiology (A&P).

Cardiac Conduction System

• Pacemaker Cells: Initiate electrical impulses in the heart.
• SA Node: Dominant pacemaker of the heart.
  • Rate: 60-100 bpm
• AV Node: Receives impulse from SA node; holds it briefly.
  • Rate: 40-60 bpm
• Bundle Branch System: Contains Purkinje fibers and the bundles of His.
  • Rate: 20-40 bpm

Backup Pacemakers

• AV Node can take over if SA Node fails, but at a slower rate (60-40 bpm).
• Bundle Branch System as the last backup (40-20 bpm).
• Decreased cardiac output at very low rates.

EKG Basics

• EKG vs. ECG: Terminology is interchangeable. Older term is EKG.
• Provides a graphic representation of the heart's electrical activity.

Obtaining an EKG

• Patient should be in a semi-reclined position, breathing normally, and electrodes should not be placed on irritated or scar tissue.
• Different types: 6-lead, 12-lead, etc.
• For this class, focus on reading EKG in Lead II.

EKG Paper

• Composed of lined boxes; each box represents time.
• Small Box: 0.04 seconds
• Large Box: 0.20 seconds
• 5 Large Boxes: 1 second
• 30 Large Boxes: 6 seconds (minimum for accurate reading)

Cardiac Cycle Components

P Wave

• Represents: Atrial depolarization (SA Node firing).
• Normal P Wave: Smooth, round, upright in Lead II, duration ≤ 0.11 seconds.
• Abnormal P Waves: Notched, peaked, inverted, indicating potential atrial issues.

QRS Complex

• Q Wave: First negative deflection after P wave; represents septal depolarization.
• R Wave: First positive deflection after Q wave; usually the tallest wave.
• S Wave: Negative deflection following the R wave.
• Normal QRS Complex: Duration 0.06 - 0.10 seconds.
• Abnormal QRS: Indicates ventricular issues.

T Wave

• Represents: Ventricular repolarization.
• Normal T Wave: Slightly asymmetric, positive deflection after QRS complex.
• Abnormal T Waves: Inverted or peaked; indicates myocardial ischemia or high potassium levels.

U Wave

• Often not seen; follows T wave, indicates possible low potassium levels.

Intervals and Segments

PR Interval

• Represents: Time from start of atrial depolarization to start of ventricular depolarization.
• Normal Duration: 0.12 - 0.20 seconds (≤ 5 small boxes).

ST Interval

• Represents: End of ventricular depolarization to beginning of repolarization.
• Abnormalities: Elevation or depression indicates myocardial ischemia/injury.

Summary

• Reviewed components of EKG and their significance.
• Importance in identifying potential cardiac issues like dysrhythmias and ischemia.
• Recommended further study from the textbook chapter on cardiac dysrhythmias.